Well, I found the Wilton instructions on their site, but it doesn't look like what you are trying to achieve. I am gonna post it incase it gives you ideas.
http://www.wilton.com/recipes/recipesandprojects/add_pans/rollercoast.cfm
And here is the link to the rollercoaster cakes in the CC galleries...
http://www.cakecentral.com/modules.php?name=gallery&meta=search&type=full&search=rollercoaster
Here is a cake where she carved the race track out of the side of the tiers. Don't see why that wouldn't work for a roller coaster!
http://www.cakecentral.com/cake-photo_32592.html
Here's another one...
http://www.cakecentral.com/cake-photo_94878.html
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